TWINNING IN OTHER SPECIES OF ARMADILLO 83 



There is evidence that En phr actus villosiis ma>' be 

 evolving toward a uniparous condition, for single fetuses 

 occur in about 15 per cent of the cases observed by 

 Fernandez. This author also observes that the uterus 

 of a young female is distinctly bicornate in structure, a 

 fact that may serve as evidence that multiple gestation 

 was the primitive condition and that the occurrence 

 of a single birth is a modern tendency resulting from the 

 gradual transformation of the uterus from the primitive 

 bicornate form into the simple form. 



Two closely allied species of Dasypus, D. sexcinctus 

 (the six-banded armadillo) and D. gymnarus (the one- 

 banded armadillo), have been described by von Kolliker 

 and by Chapman as normally uniparous, but Carson in 

 a letter states that he had a female D. sexcinctus in the 

 Philadelphia Zoological Garden that in three successive 

 pregnancies produced twins twice and a single fetus 

 once. Evidently then twinning is quite common 

 among the armadillos and is probably the normal 

 condition in many. In the Httle three-banded arma- 

 dillo, Tolypeutes conurus, the uniparous condition is 

 evidently typical, as Fernandez says of it: ''AUe 

 trachtigen uteri des Mataco (Tolypeutes conurus) fiihren 

 nur einen Embryo." He does not state, however, 

 upon how many cases this statement is based. 



One may infer then that the earliest ancestors of 

 the modern armadillos had bicornate uteri and had 

 multiple offspring; that the next step was a shortening 

 of the horns and a tendency to produce twins; that 

 with the development of a simplex uterus there came a 

 tendency to produce single offspring, which, in some 

 species has become a specific character. In the genus 



